A known noise cancelling device involves active noise control as a technique for reducing noise generated from a noise source and propagating in a space (noise propagation space). The active noise control is a technique for actively reducing noise by outputting a cancelling sound having an antiphase to the phase of the noise and having an amplitude identical with the amplitude of the noise.
As a conventional technique (for example, see Document 1 “JP H07-219563 A”), a configuration is disclosed in which a least mean square (LMS) algorithm is used to update the filter coefficient of a finite impulse response (FIR) adaptive digital filter, thereby generating a cancelling sound. The LMS algorithm calculates the filter coefficient by using an update parameter (step size parameter: parameter defining the magnitude of a correction amount in repetition). In the conventional technique, noise is a target to be cancelled, and when sounds (disturbance sounds) other than the noise are loud, the value of the update parameter is reduced to increase resistance to the disturbance sound, whereas when the disturbance sounds are small, the value of the update parameter is increased to enhance noise cancellation performance.
In general, noise fluctuates depending on environmental conditions such as temperatures, humidity, and atmospheric pressures. For example, noise of a range hood device fluctuates depending on changes in static pressure, changes in temperature, etc. in a duct. However, the disturbance sounds in the above-described conventional technique are sounds generated independently of the noise which is a target to be cancelled. In the conventional technique, it has been difficult to cancel the noise which fluctuates depending on changes in environmental conditions.